I think it's hard to "make money" in baseball cards, especially once the prices get high. It's hard to imagine what it would take to make a $1,000 card become a $1,500 card.

On the other hand, I think it's possible to do ok if you buy a particular prospect's cards in bulk (at next-to-nothing prices). For example, last summer I bought about 250 Bowman paper/chrome Avisail Garcia cards. I paid about .10 to .15 a piece (about $30ish total). I'm not especially confident that these base cards are ever going to have a cash value of more than a couple bucks, but if they do, I could "make" a few hundred dollars, and possibly several hundred.

Obviously, this strategy backfires more often than it does not. But I figure for the price of a couple blasters, I might end up doing ok in the end.

Puig is a stock that is very high now. I have 13-14 of his and some in a lot on Ebay currently.
Ryan I agree with.
Rose RC not mentioned and one of my fav finds in PSA 7 - 8 grade
Cobb - couldn't agree more. Something about owning his cards are empirical !